High speed electrophotographic printers such as the IBM 3800 Printer, employ a large photoconductive surfaced drum or belt to sequentially deliver image panels to a transfer station. The images frequently are electronically generated with a laser, LED array or the like selectively discharging the previously charged photoconductor. Where continuous form or fanfold paper with perforations defining the boundaries between sheets are employed, the movement of the images on the drum and paper requires coordination and synchronization since the image panels are not normally placed on the photoconductor with abutting boundaries.
Thus, it is necessary to periodically stop the image receiving media and separate it from the photoconductor until the next image approaches. The media is then again accelerated and brought into contact with the photoconductor. In the past, this has meant that a substantial guard band of no printing is required on either side of the perforation, or else some means of backing the paper up and resynchronizing its position with the photoconductor is needed.
Printers like the IBM 3800 printer typically skip about one inch of paper during a paperline stop-start. Disclosed is a method for reducing the unprinted zone necessary for a stop start function of the large printer paperline. This method uses a wide transfer zone to give a greater distance for stopping and starting the paperline.
Leaving minimal unprinted area above and below a forms perforation ("print to perf") is a requirement for many high speed printer users, particularly in Europe. Machines like the IBM 3800 printer typically leave about one half inch above and below each perforation during a normal stop/start operation at the paperline. It is particularly advantageous if it is possible to reduce this distance to one sixth inch above and below the perforation boundary between sheets. The prior art approach to solving this problem is by using a backhitch sequence at the transfer station.
Consider the contemporary machine which accommodates paperlines by requiring one half inch for paperline stop and one half inch for paperline start. Several things happen during a paperline stop. First the corona is turned off and the paper is pulled from the drum after which it is decelerated and stopped. Three tenths of an inch is required to let all print leave the transfer zone before the paper is pulled from the drum. Another two tenths inch is required for deceleration. Acceleration of the paperline takes three tenths of an inch. Another two tenths inch are allowed for settling of transients and lowering the paper onto the drum. Thus the half inch guard band on either side of the perforation boundary.
One method of printing to the perf, using the above described start stop profiles, is backing the paper up after deceleration and stop. Backing the paper up is called "backhitching". In order to accomplish the one sixth inch print from the perforation, it is necessary to back the paper up seven tenths of an inch. This backing up must take place in less than 30 milliseconds and requires design of all other parts associated with the paperline accommodation to let the paper back up. This capability of backing up before restarting also requires a more complicated servo system along with specially designed elements and, at best, is not a cheap alternative.
U.S. Pat. No. 3,914,047 by Hunt et al describes a technique for determining the location of the perforation in a media and timing control over machine stations in accordance with the location of the paper perforations. This patent relates to an electrophotographic copier wherein fanfold paper is sent through the transfer station. It does not suggest any method or means of printing close to the perforation (or copying close to the perforation), nor is there any discussion of restarting the paper line after a jam. Hunt et al maintain interframe spacing to eliminate image overlap and provide a space for a splice in the media web member.
U.S. Pat. No. 4,110,027 to Sato et al in FIG. 3 shows feeding of fanfold paper through a transfer zone between two rollers, which press the fanfold paper against the photoconductor before and after the transfer corona. The two rollers are movable from the position in contact with the photoconductive drum to a position separated from the drum, and in that manner, a fanfold paper is separated from the drum. That is, a mechanism separates the transfer paper from the drum at the transfer station and then restores the transfer paper into contact with the drum. The patent contains no teachings relative to printing close to the perforations in the fanfold paper.
U.S. Pat. No. 4,423,951 to Rightmyre relates to a copy machine for copying information onto fanfold paper and, in particular, relates to a roller transfer corona which physically holds the fanfold paper against the photoconductor drum, purporting to thereby overcome the problem of image voids that exist when using conventional xerographic copying systems with folded copy paper. There is no mention of a method of starting and stopping the paper within the machine, and maintaining transfer close to the perforated edge.
U.S. Pat. No. 4,541,710 by McLeish shows another fanfold copier in which the system includes a break associated with the supply of the fanfold material in order to keep a constant tension on the fanfold paper as it moves through the machine. There is no mention of a method of starting and stopping the machine, and printing close to the perforation.